History of SNAP

The objective of the government-sponsored System for Nuclear Auxiliary Power
(SNAP) program was to develop compact, lightweight reliable atomic electric
devices for use in space, sea, and land use. Atomics International served
as the prime contractor to the government for several important facets of
the SNAP program.

The United States spent considerable effort in the late 1950s to 1960s developing
the SNAP system. Only the SNAP-10 unit was fitted with a thermoelectric
conversion system which produced electricity from the heat generated by
an on-board nuclear reactor.

The objective of the SNAP-10A reactor was to produce a minimum of 500W of
electricity for a one-year duration or longer. The SNAP system weighed less
than 950 lb, including instruments and shielding.

The SNAP reactor was designed to be remotely started and operated in space.
In this manner, any hazardous radiation associated with the nuclear
fission reaction wasn't produced until after the reactor safely reached
orbit. The hazards to ground personnel were minimized and since radioactive
fission products were not present before the reactor was operated, less
of a hazard existed during launch if an accidental reentry should have occurred.

SNAP reactors used enriched uranium fuel
with zirconuim hydride as a moderator
and liquid sodium potassium alloy as the coolant. The fuel elements were
arranged in a geometric lattice called the core assembly. A thermoelectric
pump was placed above to circulate the coolant throughout the system. Beryllium
reflectors placed on ejection springs and held in place by a reflector retainer
band were placed around the core. Following successful launch and a radio
signal from earth, the reflectors rotated into place and the fission reaction
started.

The heat from the reactor was converted directly into electricity by a thermoelectric
converter. It was the first complete reactor electrical power system of
this type to have progressed through the design, development, and flight
test stages. The thermoelectric converters were located on the cone-shaped
body below the reactor. Heat from the reactor was carried by the liquid
metal coolant and piped to heat the underside of the thermoelectric elements.
The heat then escaped into space via the cone-shaped radiator.

On April 3, 1965, the SNAP-10A was launched from Vandenberg Air Force Base
and placed into a 500 nautical mile orbit around the Earth.